This inventiion relates to lightfast disperse dyestuffs and to methods of designing and preparing such dyestuffs. In particular, this invention relates to disperse dyestuffs which are so designed that their molecular structures impart lightfastness to the dyestuff.
Disperse dyestuffs were developed for use in dyeing hydrophobic synthetic fibers such as cellulose acetate, nylon, polyester and acrylics. In recent years considerable development has been directed to producing new disperse dyestuffs with improved properties for many new applications.
One of the most important considerations in determining the suitability of dyestuffs for specific applications is lightfastness. Dyes tend to undergo photodegradation upon exposure to light, especially light in the ultraviolet spectrum, resulting in fading of the dyed textile fibers. Automobile upholstery fabrics, for example, are used in perhaps one of the most severe and demanding environments for dyestuffs. Automobile interiors may be exposed to direct sunlight over extended periods of time, and may encounter extreme high temperatures and humidities. Consequently, automobile upholstery fabrics require optimum lightfastness. Most of the disperse dyestuffs presently available do not provide the high level of lightfastness demanded in automotive applications, especially where relatively dark colors are required.
Efforts to improve the lightfastness of disperse dyed fibers have been directed primarily to the use of photostabilizer additives, such as UV absorber compounds. The most commonly used photostabilizers include benzophenones, benzotriazoles, and hindered amines. These compounds are typically applied to the fiber during the dyeing process by mixing the photostabilizer compound in the dyebath with the dyestuffs and with other conventional dyebath additives. The photostabilizer compound is adsorbed into the fibers along with the dyestuff molecules and serves to protect the dyestuff molecules from the destructive effects of the energy from absorbed UV light. The mechanisms involved in the photostabilization of a disperse dyestuff molecule by photostabilizer compounds have been extensively studied and reported in the literature and will not be treated here. Suffice it to say that in the photostabilization mechanism, it is important that the photostabilizer compound be in close proximity to the chromophoric group of the dyestuff in order that it can serve to protect the dyestuff molecule from photodegradation.